Chemically Induced Virus Resistance in Arabidopsis thaliana Is Independent of Pathogenesis-Related Protein Expression and the NPR1 Gene

Abstract

Salicylic acid (SA) treatment triggers inhibition of replication or movement of several positive-sense RNA plant viruses in tobacco. This resistance can also be stimulated by nonlethal concentrations of cyanide and antimycin A (AA) without triggering induction of pathogenesis-related PR-1 protein genes. In two ecotypes of Arabidopsis thaliana (Columbia and Nössen), SA-induced resistance to a tobamovirus, Turnip vein clearing virus (TVCV), was also induced by nonlethal concentrations of cyanide and AA without concomitant induction of PR-1 gene expression. Furthermore, chemically induced resistance to TVCV, as well as the induction of the plant mitochondrial alternative oxidase (a potential target for the chemicals), was independent of NPR1, a gene that plays a key role downstream of SA in the induction of PR proteins. The chemically induced resistance to TVCV appeared to be due to inhibition of replication at the site of inoculation. Taken together, these results show that in Arabidopsis, as in tobacco, resistance to viruses can be induced via a distinct branch of the defensive signal transduction pathway. This suggests that the existence of this virus-specific branch may be widespread among plants.

Cauliflower mosaic virus, a Compatible Pathogen of Arabidopsis, Engages Three Distinct Defense-Signaling Pathways and Activates Rapid Systemic Generation of Reactive Oxygen Species

“…Several reports indicate that treating plants with SA can inhibit the cell-to-cell movement of compatible viruses (Naylor et al, 1998;Murphy and Carr, 2002;Wong et al, 2002). We did not find this with CaMV.…”

“…Wong et al (2002) reported that, in Arabidopsis, resistance to Turnip vein clearing tobamovirus (TVCV) was inducible by SA, cyanide, and antimycin A. Resistance to tobamoviruses appears to involve NPR1-independent inhibition of virus replication at the site of inoculation (Murphy and Carr, 2002;Wong et al, 2002). In contrast, SA-induced resistance to CMV appears to inhibit virus movement (Murphy et al, 2001), suggesting that, depending on the virus, defense may operate at different levels.…”

“…However, there is no evidence to indicate whether these responses function actively during systemic virus infections or indeed whether SA signaling is involved. Moreover, PR-1 is not believed to possess antiviral activity, and SA-mediated responses to incompatible virus infections are most likely activated via an NPR1-independent pathway (Murphy et al, , 2001Kachroo et al, 2000;Wong et al, 2002). Therefore, the relationship between increased PR-1 expression and defense against virus infection, compatible and incompatible, remains unclear.…”

Mitochondrial β-Cyanoalanine Synthase Is Essential for Root Hair Formation in Arabidopsis thaliana

“…Similar observations have been reported for the effect of HCN on resistance to biotic and abiotic stresses after ethylene production. For example, cyanide enhances the resistance of tobacco (Nicotiana tabacum) and Arabidopsis leaves to tobacco mosaic virus and turnip vein clearing virus, respectively (Chivasa and Carr, 1998;Wong et al, 2002). It has also been suggested that cyanide, and not ethylene, is responsible for the resistance to blast fungus infection in young rice plants (Iwai et al, 2006).…”

Modulation of host plant immunity by Tobamovirus proteins

“…Moreover, the induction of AOX by SA was not impaired in npr1 mutant plants. Based on these findings, it was proposed that NPR1 was not involved in the SA-induced resistance against TVCV (Wong et al, 2002). The role of NPR1 during compatible virus interactions was also investigated in A. thaliana plants infected with Oilseed rape mosaic virus (ORMV) (Huang et al, 2005).…”